Decades of experimental data suggest that hematopoietic stem cells can
remain quiescent, divide, differentiate or die and further, that thes
e cell fate decisions are determined by extracellular signals provided
by the hematopoietic microenvironment (ME). Given the importance of t
he ME for regulating hematopoiesis, it is imperative that transplanted
stem cells migrate efficiently and home to appropriate niches where t
hey can receive regulatory signals. Currently the rapid engraftment se
en after transplantation of cytokine-mobilized blood-derived stem cell
s would suggest that these cells are well-equipped for homing. More re
cent concerns have now been raised by the possibility that in vitro ex
pansion of these stem cells may diminish their ability to engraft. One
possible explanation for this is that expansion protocols may alter a
dhesion molecule expression and consequently homing. Data presented in
this report indicate that expression of adhesion molecules is altered
following in vitro exposure to recombinant cytokines, and that variou
s combinations of cytokines differentially modulate adhesion molecule
expression.